( 657 )
Hence it appears, that the Hypothesis corresponds with the Observations of this Star through all Parts of the Year; for the small Differences between them seem to arise from the Uncertainty of the Observation^ which is occastoned (as I imagine) chiefly by the tremulous or undulating Motion of the Air, and of the Vapours in it; which causes the Stars Sometimes to dance to and fro, fo much that it is difficult to judge when they are exactly on the Middle of the Wire that is fixed in the common Focus of the Glasses of the Telescope.
I must confefs to you, that the Agreement of the Observations with each other, as well as with the Hypothesis, is much greater than I expected to find, before I had compared them; and it may possibly be thought to be too great, by thoSe who have been uSed to Astronomical Observations, and know how difficult it is to make fuch as are in all refpects exact. But if it would be any Satisfaction to fuch Perfons (till I have an Opportunity of describing my Instrument and the manner of using it) I could assure them, that in above 70 Observations which I made of this Star in a Year, there is but one (and that is noted as very dubious on account of Clouds) which differs from the foregoing Hypothesis more than 2", and this does not differ 3".
This therefore being the Fact, I cannot but think it very probable, that the Phanomena proceed from the Caufe 1 have affigned, Since the foregoing Observations make it sufficiently evident, that the Effect of the real Cause, whatever it is, varies in this Star, in the fame Proportion that it ought according to the Hypothesis.
But least y 'Draconis may be thought not fo proper to shew the Proportion, in which the apparent Altera-
Sfff tion
( 658 )
tion of Declination is increased or diminished, as thofe Stars which lie near the Equinoctial Colure: I will give you alSo the Comparison between the Hypothesis and the Observations of n Ursae Majoris, that which was farthest South about the 17th Day of January 1728, agreeable to the Hypothesis. The following Table shews how much more Northerly it was found by Observation in Several Parts of the Year, and alSo what the Difference should have been according to the Hypothefis.
|
172*7. d. |
The Difference of Declination byOb-fervation. ^ |
The Difference of Declination by. the Hypothefis. • ^ |
1728. d. |
The Difference of Declination byOb-fervat'ion. |
SDH 3 S.aT i-5’a ^ P M. ^ O n' " * a cr P *•<1 0 «n // s '■ |
|
September - 14 |
z8i |
dpril - - 16 |
18 f |
18 | |
|
- - - 24 |
Hi |
Zfi |
May - - y |
24 i |
*3* |
|
Ottober — i<5 |
1 Pi |
191 |
'June - - f |
32 |
3 1 i |
|
November - 11 |
"i |
101 |
- - - zy |
3f |
34* |
|
December - 14 |
4 |
3 |
July - - 17 |
3<5 |
3^ |
|
1728 | |||||
|
February - 17 |
2 |
3 |
Jugufi - 2 |
3T |
3fi |
|
March - - 2; |
11* |
10' |
September - zo |
16] |
I find upon Examination, that the Hypothefis a-grees altogether as exadtly with the Observations of this Star, as the former; for in about fo that were made of it in a Year, I do not meet with a Difference of fo much as z<', except in one, which is
mark'd
